Living anionic polymers are well known in the art but truly living cationic systems have only been developed more recently. By definition, termination and chain transfer rates are zero, or negligible, in such a living polymer so that the concentration of active centers remains approximately constant. Of particular commercial interest are living organic polymers which can be used to prepare telechelic oligomers and macromolecules having hydrolyzable silyl end groups since these can be used to formulate room temperature vulcanizable (RTV), moisture-curable sealants, caulks and adhesives, inter alia. Unlike the well known moisture-curable silicone RTVs, compositions based on polymers having a hydrocarbon backbone offer the advantage of low permeability, making them more suitable for gas barrier applications such as form-in-place gaskets, O-rings, rubber plugs/seals, and the like.
U.S. Pat. No. 4,829,130 to Licchelli et al. discloses a method for preparing silylated copolymers of isobutylene which arc crosslinkable upon exposure to moisture. In this case, isobutylene is copolymerized with a comonomer having a vinylic group attached to a silylalkyl group through a benzene ring connecting group. The product of this copolymerization is a polyisobutylene (PIB) having pendant silyl-functional groups along its main chain. However, this method does not teach the preparation of a PIB having terminal silyl functionality or the preparation of a telechelic silyl-functional PIB.
To the contrary, polymers having reactive silyl head groups were described by Kennedy et al. in Advances in Polymer Science, 43, 1-50 (1982). These workers discovered that initiators which included an SiCl or SiH group as well as cationogenic moiety could be used to polymerize cationic systems such that the silicon-functional groups survived. The cationogenic moiety studied was the benzyl chloride group (i.e., --C.sub.6 H.sub.4 --CH.sub.2 Cl) wherein .alpha.-methylstyrene was polymerized in the presence of diethyl aluminum chloride as coinitiator. In this case, however, it was observed that the amount of --SiCl detected was only a small fraction of the theoretical, especially when more than one chlorine was present in the head group. Further, although these workers suggest that the SiCl groups may survive polymerization of isobutylene, they did not obtain quantitative confirmation thereof and did not demonstrate the new initiators in connection with this monomer. Thus, Kennedy et al. then turned to the investigation of systems having SiH terminal groups, such polymers being considered more promising intermediates which presented fewer experimental difficulties.
Therefore, there is still a need for compounds which are capable of initiating a cationically polymerizable monomer to prepare a polymer having a reactive silicon-functional head group.